In a large skillet, over medium-high heat, heat 1 Tablespoon olive oil. Add chicken, garlic, lemon-pepper, oregano and salt. Cook and stir until chicken is no longer pink and is fully cooked.
Warm pitas or flatbreads in microwave for a few seconds. Then divide the warm chicken between the pita or flatbreads. Top each with diced tomato, cucumber, onion and Feta cheese. Drizzle tops with Tzatziki sauce. Enjoy!